The invention relates to a tread pattern for tires intended to be fitted on vehicles bearing heavy loads.
In order to obtain satisfactory performance in use, it is known to provide a tread with a tread pattern produced by molding and vulcanization of the rubber materials making up said tread. This tread pattern as a general rule comprises a plurality of motifs which are separated from each other by grooves intended to impart appropriate grip qualities to the tread.
A distinction is made in particular between grooves directed essentially in the longitudinal direction that is to say in the circumferential direction once the tread has been laid on a tire and grooves essentially directed in the transverse direction of the tread, that is to say in the axial direction on the tire.
For a tire fitted with a tread comprising a plurality of motifs in relief which are separated from each other by transverse grooves, towards the exit from the passage in the zone of contact of the tire with the ground, great flexing of the crown of the tire occurs, involving opening of said transverse grooves. These movements of cyclic opening (upon each rotation of the wheel) result in relative sliding between the motifs in relief and the ground which results in abnormally pronounced wear on the edges of the motifs in relief.
To limit these opening movements while maintaining the presence of transverse grooves which are necessary for the grip of the tire and for evacuating fluid present on the roadway, it is known to provide, at the time of molding the tread and the vulcanization thereof, for a plurality of rubber connecting elements to be produced by molding in order to ensure a mechanical connection between the main walls defining the grooves. In order to obtain a satisfactory mechanical effect in the case of a tread pattern for a tread for heavy-vehicle tires, it is known to form in a groove of depth P at least two connecting elements (or “rubber bridges”) extending substantially transversely to the direction of said groove, said elements extending in the groove from a depth H as far as the bottom of this groove; each of these connecting elements has an appropriate width to ensure the mechanical strength of the motifs in relief while permitting a sufficient length of ridge to be maintained whatever the level of wear of the tread.
After partial wear of the tread (and before reaching the level of wear corresponding to the operating limit of this tread), these connecting elements come into contact with the roadway and will from that moment on become worn at the same time as the tread. Starting from the moment at which the rubber connecting elements come into contact with the roadway, a particularly appreciable increase in the noise emitted by the tire was noted, for example during travel on smooth ground.